There is a tradeoff relationship between the fixing property and offset resistance of a toner used in electrophotography and the like. Accordingly, there is an objective of how to combine these two properties in designing a binder resin for a toner. Further, the toner is also required to have a storage stability which refers to a property such that toner particles do not aggregate, that is, do not block in the fixing apparatus.
In response to these demands, there has been known a technique for improving the fixing property at a low temperature by introducing a crystalline component into a binder resin composed of an amorphous resin. Since the crystalline resin is rapidly melted via its melting point to have a low viscosity, it is possible to reduce the viscosity of the resin with low thermal energies and improvement of the fixing property is expected.
As a known technique for introducing a crystalline resin into a binder resin composed of an amorphous resin, there have been proposed (i) a method of hybridization of an amorphous resin and a crystalline resin at the molecular chain level in the form of a block copolymer or a graft copolymer (for example, refer to Patent Document 1), (ii) a method of blending the combination of an amorphous resin and a crystalline resin having good compatibility with each other in a physical kneading method such as melt blending, powder blending or the like (for example, refer to Patent Document 2), (iii) a method of blending the combination of an amorphous resin and a crystalline resin having poor compatibility with each other in a physical kneading method such as melt blending, powder blending or the like (for example, refer to Patent Documents 3 and 4) and the like. In the aforementioned methods (i) and (ii), however, the compatibility between the amorphous portion and the crystalline portion is good, and numerous crystalline polymer chains that cannot crystallize remain in the amorphous portion, so that it is difficult to maintain sufficient storage stability. For that reason, there is required a step of promoting and controlling crystal growth by carrying out heat treatment at a predetermined period of time or the like in some cases (refer to Patent Document 5). Further, in the method (iii), the compatibility between the amorphous portion and the crystalline portion is insufficient so that dispersion of the crystalline resin becomes difficult and it is difficult to secure the stability of the toner properties. Further, there has also been known a method for controlling the compatibility of both components by properly adjusting the monomer composition of a crystalline polyester and an amorphous polyester, and finely dispersing with a dispersion diameter of the crystalline polyester of from 0.1 to 2 μm (for example, refer to Patent Document 6). However, even in that case, since the crystal size and distribution are also varied depending on the cooling conditions at the time of producing the binder resin and producing the toner, there is a problem in securing the stability of the toner properties. In addition, the kind of monomers which can be used and composition thereof are restricted.
Patent Document 1: JP-A-04-26858
Patent Document 2: JP-A-2001-222138
Patent Document 3: JP-A-62-62369
Patent Document 4: JP-A-2003-302791
Patent Document 5: JP-A-01-35456
Patent Document 5: JP-A-2002-287426